Before articles such as steel parts which are to be heat-treated for carbonizing, sintering, and so on, are heated in a heating chamber of a continuous furnace, they are commonly pre-heated in a preheating chamber preceding to the heating chamber.
This invention relate to a method for such preheating in a continuous furnace.
When steel articles and so on are heated in a preheating chamber of a continuous furnace to a range of temperature of about 100-700.degree. C., organic substances such as oils and so on which are contained in or adhered to the articles, are evaporated, polymerized, or decomposed, whereby deadly poisonous gases are sometimes produced, and environments are most adversely polluted.
Dioxin is one of such deadly poisonous gases. In order to prevent the production of such gases, it is recommended by Japanese Welfare Ministry in a guideline for the prevention of generation of dioxin and so on to keep a temperature of combustion higher than 800.degree. C., and to sustain a concentration of O.sub.2 at an outlet of furnace higher than 6%.
It is, however, improper to make a heating temperature in a preheating chamber of continuous furnace higher than 800.degree. C., in view of a primary object of preheating in the continuous furnace.
And moreover, it is disadvantageous to keep the preheating chamber under an excess of oxygen, because the articles preheated there would be readily oxidized.